Decades of research demonstrate that a variety of overlapping policies at city, subnational, national, and international levels is more likely to succeed than are single, overarching binding agreements. Such an evolutionary approach to policy provides essential safety nets should one or more policies fail.

The good news is that evolutionary policymaking is already happening organically. In the absence of effective national and international legislation to curb greenhouse gases, a growing number of city leaders are acting to protect their citizens and economies.
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Worldwide, we are seeing a heterogeneous collection of cities interacting in a way that could have far-reaching influence on how Earth’s entire life-support system evolves. These cities are learning from one another, building on good ideas and jettisoning poorer ones. Los Angeles took decades to implement pollution controls, but other cities, like Beijing, converted rapidly when they saw the benefits. In the coming decades, we may see a global system of interconnected sustainable cities emerging. If successful, everyone will want to join the club.

Fundamentally, this is the right approach for managing systemic risk and change in complex interconnected systems, and for successfully managing common resources – though it has yet to dent the inexorable rise in global greenhouse-gas emissions.
Rio+20 has come at a crucial juncture and is undoubtedly important. For 20 years, sustainable development has been viewed as an ideal toward which to aim. But the first State of the Planet Declaration, published at the recent mammoth science gathering Planet Under Pressure, made it clear that sustainability is now a prerequisite for all future development. Sustainability at local and national levels must add up to global sustainability. This idea must form the bedrock of national economies and constitute the fabric of our societies.

The goal now must be to build sustainability into the DNA of our globally interconnected society.